Thermodynamic aspects of flagellar activity.

Despite recent advances in the fields of cytochemistry and electron microscopy the processes which are responsible for flagellar movement, and their chemical foundations, cannot be described with any certainty. In a previous communication (Holwill & Silvester, 1965) we described the variation with temperature of the frequency of the flagellar beat in Strigomonas oncopelti and deduced thermodynamic parameters which referred to the rate-limiting chemical reaction underlying the flagellar motion. The present paper represents an extension of the previous work to the cilia and fiagella of a fairly wide variety of organisms. For each organism one can evaluate an activation enthalpy and an activation entropy that are characteristic of that particular motile system, and later we shall discuss the possible significance of these values in terms of a published model of flagellar action (Silvester & Holwill, 1965). Similar activation parameters may be calculated for some muscles and it is of interest to compare these values with those obtained for fiagella. The fine structure of cilia and flagella has been well established by electron microscopy (see Holwill, 1966, for references) although the functions of the several components are the subject of discussion. The reactivation of glycerol-extracted cilia and flagella by ATP (e.g. Brokaw, 1962, 1963; Satir & Child, 1963) has led to the suggestion that the dislocation of the terminal phosphate bond in adenosine triphosphate (ATP) may be the source of energy for their movement. The way in which the chemical energy is released in a controlled manner is uncertain, but it is accepted that a motile flagellum must possess elements for contraction and compression and, further, a means of propagating waves along its length. Cytochemical techniques in conjunction with electron microscopy have been used in attempts to discover the presence and the site of ATPase activity within the flagellum. Positive results have been obtained in some instances, but the location of the ATPase appears to vary according to the organism examined. Thus, in the cilia of a rotifer, activity is found in two well-defined sites outside the axoneme (Lansing & Lamy, 1961) while for rat spermatozoa the nine fibrils surrounding the axoneme are found to have ATPase activity (Nelson, 1962). In Tetrahymena cilia, Gibbons (1963) has found that the activity is associated with the presence of ' arms' on the peripheral fibrils of the axoneme. The sustained amplitude of beat which is observed in the flagella of many organisms implies that chemical energy is available throughout the length of the flagellum (e.g. Gray, 1955; Machin, 1958). The rate of expenditure of this energy is dependent on the ambient temperature and thus, as we have previously remarked (Holwill &